chore(compose): maintenance-long needs only /images; drop dead /downloads mounts

Operator-flagged: /downloads was never mapped in prod and everything worked —
confirmed nothing in the app references a filesystem /downloads (only the
unrelated /api/downloads route). Dropped the dead mount from web/worker/
scheduler, and scoped the new maintenance-long worker to just /images (backups
write to /images/_backups; audits + admin tasks all operate on /images).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -57,7 +57,6 @@ services:
     volumes:
       - ./images:/images
       - ./import:/import
-      - ./downloads:/downloads
       # FC-5 legacy migration: bind-mount the host's ImageRepo images dir
       # under /import (FC's existing filesystem scan picks them up). Read-only
       # is sufficient — FC copies into /images during the scan. The worker +
@@ -76,10 +75,11 @@ services:
       <<: *app_env
       CELERY_QUEUES: default,import,thumbnail,download
       CELERY_CONCURRENCY: "2"
+    # /downloads dropped — nothing in the app references it (operator-flagged
+    # 2026-06-07: it wasn't mapped in prod and everything worked).
     volumes:
       - ./images:/images
       - ./import:/import
-      - ./downloads:/downloads
     depends_on:
       postgres: { condition: service_healthy }
       redis:    { condition: service_healthy }
@@ -93,7 +93,6 @@ services:
     volumes:
       - ./images:/images
       - ./import:/import
-      - ./downloads:/downloads
     depends_on:
       postgres: { condition: service_healthy }
       redis:    { condition: service_healthy }
@@ -109,10 +108,10 @@ services:
       <<: *app_env
       CELERY_QUEUES: maintenance_long
       CELERY_CONCURRENCY: "1"
+    # Only /images: backups write to /images/_backups, audits read /images, and
+    # the admin tasks (re-extract/cascade-delete/normalize) operate on /images.
     volumes:
       - ./images:/images
-      - ./import:/import
-      - ./downloads:/downloads
     depends_on:
       postgres: { condition: service_healthy }
       redis:    { condition: service_healthy }